Martin et al., in U.S. Pat. No. 4,228,050, have disclosed an improved molding composition for the compression molding of high density information discs, also known as video discs. This molding composition is a conductive molding composition, containing sufficient conductive carbon black particles to obtain the desired conductivity (bulk resistivity below about 500 ohm-cm at 900 megahertz), along with other desired additives such as stabilizers, lubricants, plasticizers, and processing aids. The remainder of the conductive molding composition is a polyvinylchloride based resin, and the composition has the proviso that not more than about 5 percent by weight of liquid additives are present therein. Molded articles, such as high density information disc replicas, molded from this improved conductive molding composition are said to be dimensionally stable and possess improved resistance to the effects of changes in environmental temperatures and humidity.
However, we have found that the stability of these discs with respect to environmental fluctuations of temperature and relative humidity have been less than satisfactory. Discs which on initial playback have excellent or acceptable playback characteristics, deteriorate with respect to playback after storage under ambient conditions. This deterioration is particularly marked when the discs are exposed to conditions of high temperature and high relative humidity.
Huck et al. in copending application Ser. No. 091,878, filed Nov. 7, 1979, and entitled "VIDEO DISC PROCESSING" have disclosed that high density information discs which have been cleaned with an aqueous solution have improved stability of playback characteristics to changing environmental conditions. The use of water alone or dilute solutions of acids or bases are shown to remove water soluble metal salts and other water soluble materials, such as certain organic impurities, on the surface of the disc, which materials contribute to the moisture sensitivity of the disc.
Datta, in copending application Ser. No. 109,206, filed Jan. 4, 1980, entitled "VIDEO DISC PROCESSING", has disclosed that an aqueous solution comprising an oxidizing agent, a base, and a sufficient amount of a fluorosurfactant which will produce a solution having a surface tension below about 35 dynes/cm.sup.2 is an excellent cleaning solution for high density information discs. It has been shown that by the use of this aqueous cleaning solution, metal salts including calcium, barium, nickel, lead, and tin salts, sulfur compounds, and organic compounds, such as esters, which are originally present on the surface of the disc are removed from the disc surface, thereby lessening its sensitivity to moisture.
However, upon exposure to conditions of elevated temperature and relative humidity for extended periods of time, the discs deteriorate such that their playback characteristics are no longer excellent and in some cases are not even acceptable. Thus, the search has continued for better disc materials and processing to improve the stability of high density information discs to conditions of high temperature and high relative humidity, particularly exposure to such conditions for extended time periods.